Methods and Systems for Emission System Control

ABSTRACT

Methods and systems are provided for operating an engine including an emission control system, the emission control system comprising a catalyst downstream of a turbine of a boosting device and a reductant injector upstream of the turbine. In one example, the method comprises injecting reductant into exhaust upstream of the turbine, mixing the injected reductant with exhaust gas via the turbine, and delivering the mixed reductant to the catalyst.

FIELD

The present application relates to methods and systems for emissioncontrol of a vehicle with a selective catalytic reduction (SCR) catalystand a particulate filter.

BACKGROUND AND SUMMARY

Selective catalytic reduction (SCR) systems may be used in vehicles toreduce NOx emissions. SCR systems involve injection of a reductantupstream of an SCR catalyst. The reductant, or reductant products, thenreacts with exhaust NOx species to create byproducts such as nitrogenand water. The system may also include mixers to facilitate mixing ofthe injected reductant with exhaust gases before interacting with theSCR catalyst.

Various approaches may be used to control emission systems including SCRcatalysts to enable good mixing of reductant and exhaust, and minimizereductant slip from the catalyst. One example approach is illustrated byKimura et al. in JP 2008-128046A. Therein, a reductant injector isprovided downstream of a turbocharger turbine and upstream of the SCRcatalyst. Specifically, reductant is injected into an exhaust flowcoming out of the turbocharger.

However, the inventors herein have recognized several potential issueswith such an approach. As one example, reductant vaporization may besignificantly degraded due to injection into exhaust gases downstream ofthe turbocharger. In other words, significant exhaust gas heat may beextracted by the turbine thus reducing the initial vaporization uponinjection of the liquid reductant into the exhaust. Such reduction invaporization may reduce NOx conversion efficiency of the SCR catalyst,as well as result in increased reductant deposits.

In one example, the above mentioned issues may be addressed by a methodof operating an engine including an emission control system, theemission control system comprising a catalyst downstream of an exhaustturbine of a boosting device, the emission control system furthercomprising a reductant injector upstream of the turbine. In oneembodiment, the method comprises, injecting reductant to the exhaustupstream of the turbine, mixing the injected reductant with exhaust gasvia the turbine; and delivering the mixed reductant to the catalyst.

In this way, it is possible to not only improve mixing by utilizingaction of the turbine, but further it is possible to increasevaporization by injecting reductant upstream of the turbine beforeexhaust gas temperature drops due to the energy extracted by theturbine. Specifically, by injecting reductant upstream of an exhaustturbine, and by flowing the reductant through the turbine vanes andblades, a finer atomization of the reductant may be achieved.Additionally, the turbulence generated in the turbine may improve mixingof the reductant with the exhaust.

Furthermore, by injecting the reductant upstream of the turbine, some ofthe improved atomization and mixing benefits may be synergisticallyenhanced by increased vaporization due to the higher exhaust gastemperature upstream of the turbine as compared with downstream of theturbine. Yet, at the same time, by positioning the SCR catalystdownstream of the turbine, an appropriate temperature regime for the SCRcatalyst can still be maintained.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic depiction of an internal combustion engine andan associated emission control system.

FIG. 2 shows a partial engine view.

FIGS. 3A-B show a high level flow chart for operating the emissioncontrol system of FIG. 1, according to the present disclosure.

FIG. 4 shows a high level flow chart for addressing boost issues atdriver tip-in based on filter regeneration conditions.

FIG. 5 shows a high level flow chart for addressing reductant mixingissues.

FIG. 6 shows a high level flow chart for controlling the temperature ofa downstream SCR catalyst by adjusting an upstream wastegate.

FIG. 7 shows a high level flow chart for adjusting reductant injectionbased on boost.

FIG. 8 shows a high level flow chart for adjusting exhaust gasrecirculation based on filter regeneration conditions.

DETAILED DESCRIPTION

The following description relates to systems and methods for operatingan emission control system associated with a turbocharged internalcombustion engine. As shown in FIGS. 1-2, the emission control systemincludes a catalyst, such as an SCR catalyst, downstream of theturbocharger turbine, and a particulate filter, such as a dieselparticulate filter (DPF), upstream of the turbine. A controller may beconfigured to perform a control routine, such as the routine of FIGS.3A-B to coordinate the operation of the various emission control deviceswith each other, and with other engine operations such as exhaust gasrecirculation and boosting.

The emission control system also includes a reductant injector upstreamof the turbine. By injecting reductant upstream of the turbine andmixing the injected reductant with exhaust gas via the turbine, thevaporization of the reductant may be improved. At the same time, bypositioning the catalyst downstream of the turbine, the well-mixedreductant may be delivered to the catalyst without affecting thetemperature characteristics of the catalyst. A controller may beconfigured to perform a control routine, such as the routine of FIGS. 5and 7 to adjust the amount of reductant injected based on operatingconditions, such as an amount of boost provided by the turbocharger, andto adjust the turbocharger wastegate to enable improved mixing of theinjected reductant with exhaust gases.

By including a particulate filter upstream of the turbocharger,additional benefits may be achieved. For example, turbo lag conditionsmay be addressed synergistically during filter regeneration. Byinjecting fuel into one or more engine cylinders via a late postinjection in an exhaust stroke of the engine cycle, the temperature ofthe exhaust gas may be increased before spooling up the turbochargerturbine. By increasing the exhaust temperature, the filter may beregenerated while the exhaust also increases turbine speed and reducesturbo lag. A controller may be configured to perform control routines,such as the routine of FIG. 4, to adjust the timing and/or amount of theinjection based on the amount of heat needed to increase the temperatureof the particulate filter for regeneration and/or the amount of heatneeded to increase the turbine speed to provide the desired torque.

By positioning the filter upstream of the turbine, and the catalystdownstream of the turbine, temperature control and coordination betweenthe emission control devices may also be achieved. For example, thetemperature of the SCR catalyst may be maintained even while the filteris being regenerated. A controller may be configured to perform controlroutines, such as the routine of FIG. 6, to adjust a turbine wastegateduring filter regeneration to adjust an exhaust flow that is directedtowards the SCR catalyst. In this way, the temperature of the SCRcatalyst may be controlled during the different filter operating modes.

The engine system may further include one or more EGR passages forrecirculating at least some exhaust gas into the engine intake. Forexample, an EGR passage may divert exhaust gas from upstream of theturbine and downstream of the particulate filter into the engine intakedownstream of the compressor. By positioning the particulate filterupstream of the turbocharger turbine and upstream of the EGR passageinlet, both EGR and particulate filter benefits may be achieved. Thus,when EGR is desired, more exhaust gas may be recirculated through theEGR passage after passing through the filter, thereby providing a cleanEGR flow to the intake. In this way, EGR cooler, EGR valve, intakemanifold, and intake valve degradation may be reduced, for example.Then, when filter regeneration is desired, less exhaust gas may berecirculated through the EGR passage after passing through the filter,thereby reducing engine performance degradation due to hot EGR flow. Acontroller may be configured to perform control routines, such as theroutine of FIG. 8, to adjust an amount of EGR flow based on filteroperation, to thereby coordinate the EGR system with the emissioncontrol system.

FIG. 1 shows a schematic depiction of a vehicle system 6. The vehiclesystem 6 includes an engine system 8, including engine 10, coupled toemission control system 22. Engine 10 includes a plurality of cylinders30. Engine 10 also includes an intake 23 and an exhaust 25. Intake 23includes a throttle 62 fluidly coupled to the engine intake manifold 44via intake passage 42. Exhaust 25 includes an exhaust manifold 48leading to an exhaust passage 45 that routes exhaust gas to theatmosphere via tailpipe 35.

Engine 10 may further include a boosting device, such as turbocharger50. Turbocharger 50 may including a compressor 52 arranged along intakepassage 42. The compressor 52 may be at least partially driven byturbine 54, arranged along exhaust passage 45, via shaft 56. The amountof boost provided by the turbocharger may be varied by an enginecontroller. For example, the amount of boost may be adjusted bycontrolling wastegate 58. In one example, the amount of boost may bedecreased by opening wastegate 58 and allowing more exhaust gas toby-pass the turbine. Alternatively, the amount of boost may be increasedby closing the wastegate (or reducing the opening of the wastegate) andallowing less exhaust gas to by-pass the turbine. In other examples,turbine 54 may be a variable geometry turbine (VGT) or a variable nozzleturbine (VNT). The VGT or VNT may be adjusted to meet boostrequirements. Further, the wastegate, VNT, and/or VGT may be adjusted toprevent overspeed conditions from occurring in the turbocharger. In someembodiments, an optional charge after-cooler 34 may be includeddownstream of compressor 52 in intake passage 42. The after-cooler maybe configured to reduce the temperature of the intake air compressed byturbocharger 50.

Emission control system 22, coupled to exhaust passage 45, may includeone or more emission control devices 69 mounted in a close-coupledposition in the exhaust. One or more emission control devices mayinclude particulate filter 72, SCR catalyst 76, three-way catalyst, leanNOx trap, oxidation catalyst, etc. The emission control devices may bepositioned upstream and/or downstream of turbine 54 in exhaust passage45. In one embodiment, as depicted, particulate filter 72 may bepositioned upstream of turbocharger turbine 54 while SCR catalyst 76 maybe positioned downstream of turbocharger turbine 54. In one example,particulate filter 72 may be an uncoated diesel particulate filter. Inalternate embodiments, particulate filter 72 may include a catalyticwashcoat. Catalytic washcoats used may include, for example, palladium,a hydrocarbon adsorbent (such as activated carbon or zeolite), an SCRcatalyst, a HC adsorbent-SCR catalyst combination, etc.

Reductant injector 80, positioned upstream of turbocharger turbine 54,may inject reductant 82, such as urea or ammonia, into the exhaust forreaction with NOx species in the SCR catalyst 76. Specifically, injector80 may inject reductant 82 into the exhaust upstream of turbine 54 anddownstream of particulate filter 72, responsive to signals received fromthe engine controller. By injecting reductant upstream of the turbine,and delivering the injected reductant to the SCR catalyst via theturbine, the vaporization of the reductant and the mixing of thereductant with exhaust gases may be improved. As elaborated withreference to FIG. 5, the wastegate of the turbine may be adjusted tocontrol an amount of mixing of the reductant with exhaust gases.Further, as elaborated herein with reference to FIG. 7, an amount and/ortiming of reductant injection may be adjusted based on engine operatingconditions such as changes in boost, and changes in wastegate positions.In alternate embodiments, reductant injector 80 may be positioneddownstream of turbine 54.

Engine 10 may further include one or more exhaust gas recirculation(EGR) passages for recirculating at least a portion of exhaust gas fromthe engine exhaust (specifically, exhaust passage 45) to the engineintake (specifically, intake passage 42). In one embodiment, a first EGRsystem 60 and a second EGR system 70 may be included. Specifically,first EGR system 60 may divert a portion of exhaust gas from upstream ofturbine 54, and downstream of filter 72, to the engine intake downstreamof compressor 52 via HP-EGR passage 63. In this configuration, first EGRsystem 60 may provide high-pressure EGR (HP-EGR). Second EGR system 70may divert a portion of exhaust gas from downstream of turbine 54 to theengine intake upstream of compressor 52 via LP-EGR passage 73. In thisconfiguration, second EGR system 70 may provide low-pressure EGR(LP-EGR). In one example, HP-EGR system 60 may be operated during afirst condition, such as in the absence of boost provided byturbocharger 50, while LP-EGR system 70 may be operated during a secondcondition, such as in the presence of turbocharger boost and/or whenexhaust gas temperature is above a threshold. In other examples, bothHP-EGR system 60 and LP-EGR system 70 may be operated simultaneously.

Each EGR passage may further include an EGR cooler. For example, HP-EGRsystem 60 may include HP-EGR cooler 64 while LP-EGR system 70 mayinclude LP-EGR cooler 74. HP-EGR cooler 64 and LP-EGR cooler 74 may beconfigured to lower the temperature of exhaust gas flowing through therespective EGR passages before recirculation into the engine intake.Under certain conditions, the LP-EGR cooler 74 may be used to heat theexhaust gas flowing through LP-EGR system 70 before the exhaust gasenters the compressor to avoid water droplets impinging on thecompressor. In some embodiments, one or more of the EGR cooler channelsmay be coated with an SCR catalyst to enable additional exhausttreatment before recirculation to the intake.

While the depicted embodiment illustrates LP-EGR passage 73 diverting atleast a portion of exhaust gas from downstream of SCR catalyst 76, inalternate embodiments, LP-EGR passage 73 may be configured to divert atleast a portion of exhaust gas from upstream of SCR catalyst 76. In oneexample, by diverting exhaust gas from upstream of SCR catalyst 76 tothe engine intake, EGR passage plumbing may be shortened whileincreasing the pressure difference available. In still otherembodiments, one or more catalysts (e.g., an SCR catalyst and/or adiesel oxidation catalyst) may be included in LP-EGR passage 73, forexample, upstream of LP-EGR cooler 74. An exhaust back-pressure valvemay optionally also be included. Alternatively, an intake throttledisposed in the intake upstream of the compressor may be used instead ofan exhaust throttle. In one example, by including an SCR in LP-EGRpassage 73, and diverting exhaust gas from upstream of SCR catalyst 76,at least some injected reductant (for example, excess of a thresholdamount) may be stored in the SCR, to reduce ammonia slip without NOxremake. However, by including an oxidation catalyst in LP-EGR passage73, and diverting exhaust gas from upstream of SCR catalyst 76, at leastsome injected reductant (for example, excess of a threshold amount) maybe consumed on the oxidation catalyst, to reduce ammonia slip withoutNOx remake.

In one example, HP-EGR system 60 may divert a portion of exhaust gasdownstream of the compressor upstream of charge air cooler 34. Inanother example, HP-EGR system 60 may divert a portion of exhaust gasdownstream of the compressor downstream of charge air cooler 34. In oneembodiment, HP-EGR system 60 may further include a bypass passage (notshown) configured to divert a portion of exhaust gas from HP-EGR passage63, upstream of HP-EGR cooler 64, to the engine intake, downstream ofcharge air cooler 34, thereby bypassing both coolers. In this way, bybypassing both the HP-EGR cooler and the compressor charge air cooler,heated exhaust may be directed to the engine intake without cooling,when desired, to expedite engine warm-up. Additionally, HP-EGR coolerfouling may be reduced.

An engine controller 12 may adjust an amount (and/or rate) of exhaustgas diverted via the EGR passage(s) based on engine operatingconditions, exhaust gas temperature, intake manifold temperature, anoperating mode of the particulate filter (or a degree of filterregeneration), catalyst conditions, etc. Each EGR passage may include anEGR valve, and the controller 12 may be configured to adjust an amountof diverted exhaust gas by adjusting the opening of the respective EGRvalve. For example, an amount and/or rate of HP-EGR provided to intakemanifold 44 may be adjusted via HP-EGR valve 29. HP-EGR sensor 65 may bepositioned within HP-EGR passage 63 to provide an indication of one ormore of a pressure, temperature, composition, and concentration ofexhaust gas recirculated through HP-EGR system 60. Similarly, an amountand/or rate of LP-EGR provided to intake passage 42 may be varied bycontroller 12 via LP-EGR valve 39. LP-EGR sensor 75 may be positionedwithin LP-EGR passage 73 to provide an indication of one or more of apressure, temperature, composition, and concentration of exhaust gasrecirculated through LP-EGR system 70.

In some examples, one or more sensors may be used to determine a totalamount of exhaust gas flowing through the HP-EGR and LP-EGR systems. Forexample, an UEGO sensor may be positioned within intake passage 42downstream of the HP-EGR system outlet to determine a total amount ofEGR. For example, total EGR control may be based on intake oxygenconcentration or a burned mass fraction, since intake oxygenconcentration may be directly related to EGR corrected for exhaustoxygen concentration.

Under some conditions, exhaust gas recirculation through HP-EGR system60 and/or LP-EGR system 70 may be used to regulate the temperature ofthe air and fuel mixture within the intake manifold, and/or reduceNO_(x) formation of combustion by reducing peak combustion temperatures,for example. As elaborated herein with reference to FIG. 8, under someconditions, for example during particulate filter 72 regeneration and/orwhen exhaust gas temperature is above a threshold, the amount of exhaustgas diverted to the engine intake along EGR passage 63 may be reduced toreduce engine performance degradation due to hot EGR flow. By divertingexhaust gas from upstream of the turbine and downstream of theparticulate filter, advantageous synergies between the emission controlsystem and the EGR system may be achieved. For example, exhaust gas maybe cleaned upon passage through the filter. Thus, clean exhaust gas,from which particulate matter has been substantially removed, may bediverted to the engine intake, thereby reducing intake manifold and EGRcooler and valve fouling due to exhaust particulates, for example.

Engine 10 may be controlled at least partially by a control system 14including controller 12 and by input from a vehicle operator via aninput device (not shown). Control system 14 is shown receivinginformation from a plurality of sensors 16 (various examples of whichare described herein) and sending control signals to a plurality ofactuators 81. As one example, sensors 16 may include exhaust gas sensor126 located upstream of the emission control device, exhaust temperaturesensor 128 and exhaust pressure sensor 129 located downstream of theemission control system in tailpipe 35, HP-EGR sensor 65 located inHP-EGR passage 63, and LP-EGR sensor 75 located in LP-EGR passage 73. Insome examples, sensors 16 may include one or more sensors used todetermine a total amount of EGR, for example based on burned massfraction and/or intake oxygen. Other sensors such as additionalpressure, temperature, air/fuel ratio and composition sensors may becoupled to various locations in the vehicle system 6. As anotherexample, actuators 81 may include fuel injector 66, HP-EGR valve 29,LP-EGR valve 39, throttle 62, reductant injector 80, and wastegate 58.Other actuators, such as a variety of additional valves and throttles,may be coupled to various locations in vehicle system 6. Controller 12may receive input data from the various sensors, process the input data,and trigger the actuators in response to the processed input data basedon instruction or code programmed therein corresponding to one or moreroutines. Example control routines are described herein with regard toFIGS. 3-8.

FIG. 2 depicts an example embodiment of a combustion chamber or cylinderof internal combustion engine 10. Engine 10 may be controlled at leastpartially by a control system including controller 12 and by input froma vehicle operator 130 via an input device 132. In this example, inputdevice 132 includes an accelerator pedal and a pedal position sensor 134for generating a proportional pedal position signal PP. Cylinder (i.e.combustion chamber) 30 of engine 10 may include combustion chamber walls136 with piston 138 positioned therein. Piston 138 may be coupled tocrankshaft 140 so that reciprocating motion of the piston is translatedinto rotational motion of the crankshaft. Crankshaft 140 may be coupledto at least one drive wheel of the passenger vehicle via a transmissionsystem. Further, a starter motor may be coupled to crankshaft 140 via aflywheel to enable a starting operation of engine 10.

Cylinder 30 can receive intake air via a series of intake air passages142, 144, and 146. Intake air passage 146 can communicate with othercylinders of engine 10 in addition to cylinder 30. In some embodiments,one or more of the intake passages may include a turbocharger includinga compressor 52 arranged between intake air passages 142 and 144, and anexhaust turbine 54 arranged along exhaust passage 148. Compressor 52 maybe at least partially powered by exhaust turbine 54 via shaft 56. Insome embodiments, shaft 56 may be coupled to an electric motor toprovide an electric boost, as needed. A throttle 62 including a throttleplate 164 may be provided along an intake passage of the engine forvarying the flow rate and/or pressure of intake air provided to theengine cylinders. For example, throttle 62 may be disposed downstream ofcompressor 52, as shown, or may be alternatively provided upstream ofcompressor 52. In some examples, throttles may be disposed both upstreamand downstream of compressor 52.

Exhaust passage 148 can receive exhaust gases from other cylinders ofengine 10 in addition to cylinder 30. Exhaust gas sensor 126 is showncoupled to exhaust passage 148 upstream of emission control device 69.Sensor 126 may be any suitable sensor for providing an indication ofexhaust gas air/fuel ratio such as a linear oxygen sensor or UEGO(universal or wide-range exhaust gas oxygen), a two-state oxygen sensoror EGO (as depicted), a HEGO (heated EGO), a NOx, HC, or CO sensor. Insome examples, sensor 126 may be coupled to the exhaust passagedownstream of turbine 52 and emission control device 69. Emissioncontrol device 69 may be a three way catalyst (TWC), NOx trap, variousother emission control devices, or combinations thereof. For example,emission control device 69 may include SCR catalyst 76 positioneddownstream of turbine 54. SCR catalyst 76 may be configured to reduceexhaust NOx species to nitrogen upon reaction with reductant, such asammonia or urea. Reductant injector 80 may inject reductant 82 intoexhaust passage 148 upstream of turbine 54. Exhaust passage 148 may alsoinclude a particulate filter 72, positioned upstream of turbine 54 andinjector 80, for removing particulate matter from exhaust gas.

Each cylinder of engine 10 may include one or more intake valves and oneor more exhaust valves. For example, cylinder 30 is shown including atleast one intake poppet valve 150 and at least one exhaust poppet valve156 located at an upper region of cylinder 30. In some embodiments, eachcylinder of engine 10, including cylinder 30, may include at least twointake poppet valves and at least two exhaust poppet valves located atan upper region of the cylinder.

Intake valve 150 may be controlled by controller 12 via actuator 152.Similarly, exhaust valve 156 may be controlled by controller 12 viaactuator 154. During some conditions, controller 12 may vary the signalsprovided to actuators 152 and 154 to control the opening and closing ofthe respective intake and exhaust valves. The position of intake valve150 and exhaust valve 156 may be determined by respective valve positionsensors (not shown). The valve actuators may be of the electric valveactuation type, cam actuation type, electro-hydraulic type, or acombination thereof. The intake and exhaust valve timing may becontrolled concurrently or any of a possibility of variable intake camtiming, variable exhaust cam timing, dual independent variable camtiming or fixed cam timing may be used. Each cam actuation system mayinclude one or more cams and may utilize one or more of cam profileswitching (CPS), variable cam timing (VCT), variable valve timing (VVT)and/or variable valve lift (VVL) systems that may be operated bycontroller 12 to vary valve operation. For example, cylinder 30 mayalternatively include an intake valve controlled via electric valveactuation, and an exhaust valve controlled via cam actuation includingCPS and/or VCT. In other embodiments, the intake and exhaust valves maybe controlled by a common valve actuator or actuation system, or avariable valve timing actuator or actuation system. The engine mayfurther include a cam position sensor whose data may be merged with thecrankshaft position sensor to determine an engine position and camtiming.

Cylinder 30 can have a compression ratio, which is the ratio of volumeswhen piston 138 is at bottom center to top center. Conventionally, thecompression ratio is in the range of 9:1 to 10:1. However, in someexamples where different fuels are used, the compression ratio may beincreased.

In some embodiments, each cylinder of engine 10 may include a spark plug192 for initiating combustion. Ignition system 190 can provide anignition spark to combustion chamber 30 via spark plug 192 in responseto spark advance signal SA from controller 12, under select operatingmodes. However, in some embodiments, spark plug 192 may be omitted, suchas where engine 10 may initiate combustion by auto-ignition or byinjection of fuel as may be the case with some diesel engines.

In some embodiments, each cylinder of engine 10 may be configured withone or more fuel injectors for providing fuel thereto. As a non-limitingexample, cylinder 30 is shown including fuel injector 166 coupleddirectly to cylinder 30. Fuel injector 166 may inject fuel directlytherein in proportion to the pulse width of signal FPW received fromcontroller 12 via electronic driver 168. In this manner, fuel injector166 provides what is known as direct injection (hereafter referred to as“DI”) of fuel into combustion cylinder 30. While FIG. 2 shows injector166 as a side injector, it may also be located overhead of the piston,such as near the position of spark plug 192. Alternatively, the injectormay be located overhead and near the intake valve. Fuel may be deliveredto fuel injector 166 from high pressure fuel system 172 including a fueltank, fuel pumps, and a fuel rail. Alternatively, fuel may be deliveredby a single stage fuel pump at lower pressure. Further, while not shown,the fuel tank may have a pressure transducer providing a signal tocontroller 12.

It will be appreciated that in an alternate embodiment, injector 166 maybe a port injector providing fuel into the intake port upstream ofcylinder 30. It will also be appreciated that cylinder 30 may receivefuel from a plurality of injectors, such as a plurality of portinjectors, a plurality of direct injectors, or a combination thereof.

Controller 12 is shown in FIG. 2 as a microcomputer, includingmicroprocessor 106, input/output ports 108, an electronic storage mediumfor executable programs and calibration values shown as read-only memory110 in this particular example, random access memory 112, keep alivememory 114, and a data bus. Controller 12 may receive various signalsfrom sensors coupled to engine 10, in addition to those signalspreviously discussed, including measurement of inducted mass air flow(MAF) from mass air flow sensor 122; engine coolant temperature (ECT)from temperature sensor 116 coupled to cooling sleeve 118; a profileignition pickup signal (PIP) from Hall effect sensor 120 (or other type,such as a crankshaft position sensor) coupled to crankshaft 140;throttle position (TP) from a throttle position sensor (not shown); andabsolute manifold pressure signal (MAP) from sensor 124. Engine speedsignal, RPM, may be generated by controller 12 from signal PIP (or thecrankshaft position sensor). Manifold pressure signal MAP from amanifold pressure sensor may be used to provide an indication of vacuum,or pressure, in the intake manifold. Storage medium read-only memory 110can be programmed with computer readable data representing instructionsexecutable by microprocessor 106 for performing the methods describedbelow as well as other variants that are anticipated but notspecifically listed.

One or more exhaust gas recirculation (EGR) passages (as illustrated inFIG. 1) may route a desired portion of exhaust gas from exhaust passage148 to intake passage 144. For example, a portion of exhaust gas thathas been filtered through particulate filter 72 may be diverted tointake passage 144 via EGR passage 63. The amount of EGR flow providedto the intake may be varied by controller 12 via EGR valve 29. An EGRsensor (not shown) may be arranged within EGR passage 63 and may providean indication of one or more of a pressure, temperature, andconcentration of the exhaust gas. Under some conditions, the EGR systemmay be used to regulate the temperature of the air and fuel mixturewithin the combustion chamber, thus providing a method of controllingthe timing of ignition during some combustion modes.

As described above, FIG. 2 shows only one cylinder of a multi-cylinderengine. As such each cylinder may similarly include its own set ofintake/exhaust valves, fuel injector(s), spark plug, etc.

Now turning to FIGS. 3A-B, a routine 300 is depicted for coordinatingthe operation of the emission control system of FIG. 1 with turbochargeroperations and EGR operations. Specifically, routine 300 enablesadjustments to a turbocharger wastegate, in view of particulate filterregeneration, to control an SCR catalyst temperature and improvereductant mixing. The routine also enables wastegate adjustments, inview of filter regeneration, to thereby adjust an amount of exhaust gasrecirculated via HP-EGR and LP-EGR. Further, the routine compensates forthe wastegate adjustments, for example, through reductant injection andthrottle position adjustments.

At 302, engine operating conditions may be measured and/or estimated.These may include, for example, a catalyst temperature (Tcat), forexample, of SCR catalyst 76, a filter temperature (Tfil), for example,of particulate filter 72, engine speed (Ne), exhaust NOx levels, exhausttemperature, an amount of torque requested by the driver, etc.Additional SCR catalyst and filter conditions may also be estimated, forexample, an amount of reductant stored on the SCR catalyst and/or anamount of particulates stored in the filter.

At 304, based on the estimated engine operating conditions and therequested torque, an amount of boost required to provide the requestedtorque may be determined. At 306, initial EGR settings may be determinedbased on the estimated exhaust NOx levels and exhaust temperatures toprovide a desired EGR flow. For example, an initial ratio of HP-EGR toLP-EGR may be determined to provide a desired EGR temperature ormanifold air temperature. The initial ratio of HP-EGR to LP-EGR may alsodepend on compressor inlet temperature to avoid over temperatureconditions as well as mass flow and pressure ratio to avoid surge andchoke. The initial ratio of HP-EGR and LP-EGR may enable at least someexhaust gas to be diverted to the engine intake system (downstream ofthe turbocharger compressor) from downstream of the particulate filterand upstream of the turbine while also enabling at least some exhaustgas to be diverted to the engine intake system (upstream of theturbocharger compressor) from downstream of the particulate filter anddownstream of the turbine. The initial EGR settings determined mayinclude flow rates, valve positions, EGR cooler settings, etc. At 308,based on the desired boost, an initial wastegate position may bedetermined.

At 310, it may be determined whether any boost issues have arisen inresponse to a driver tip-in. If no boost issues have arisen, the routinemay directly proceed to 314. If boost issues are present, at 312, theroutine may address the boost issues with a late fuel injection andwastegate adjustments, as further elaborated in FIG. 4, beforeproceeding to 314. At 314, it may be determined whether the injectedreductant has sufficiently mixed with exhaust gases. If no mixing issueshave arisen, the routine may directly proceed to 318. If mixing issuesare present, at 316, the routine may address the mixing issues withfurther wastegate adjustments, as further elaborated in FIG. 5, beforeproceeding to 318. At 318, it may be determined whether the SCR catalysttemperature is within the desired operating range. If no temperatureissues have arisen, the routine may directly proceed to 322. If thetemperature is outside the range, at 320, the routine may address thecatalyst temperature issues with further wastegate adjustments, asfurther elaborated in FIG. 6, before proceeding to 322.

At 322, the routine may determine a final wastegate position based onadjustments determined at 312, 316, and 320. In one example, the routinemay prioritize the wastegate adjustments by giving each adjustment adifferent weightage. For example, wastegate adjustments responsive toSCR catalyst temperature issues and/or turbocharger overspeed conditionsmay be given higher weightage over wastegate adjustments responsive toboost issues. In one example, it may determined that SCR catalysttemperature issues may be addressed by increasing the wastegate opening,while at the same time it may be determined that boost issues may beaddressed by decreasing the wastegate opening. Herein, in one example,the routine may over-ride the wastegate adjustments responsive to boostissues and increase the wastegate opening by a first, larger, amount toaddress the catalyst temperature issues only. In another example, theroutine may consider the wastegate adjustments required to address theboost issues and increase the wastegate opening by a second, smaller,amount to address both issues. In still other examples, the adjustmentsto the different issues may be given equal weightage.

At 324, the routine may adjust an amount of reductant injected upstreamof the turbine based on the final wastegate position. As furtherelaborated in FIG. 7, the reductant injection may be adjusted based on achange in boost arising from changes in wastegate position. At 326,other engine operating parameters may be adjusted to compensate for thewastegate adjustments. These may include, for example, changes inthrottle position, changes in valve/cam timing, changes in spark timing,etc.

At 328, it may be determined whether EGR is present and whether theparticulate filter is also regenerating at the same time. If both an EGRoperation and a filter regeneration operation is confirmed, then at 328,a ratio of HP-EGR and LP-EGR may be adjusted based on the engineoperating conditions, as further elaborated in FIG. 8.

In this way, the operation of emission control devices such as SCRcatalysts and particulate filters may be coordinated with boost and EGRoperations.

Now turning to FIG. 4, a routine 400 is illustrated for adjusting anamount of fuel that is late injected into the engine, based on filterregeneration and selected boosted operating conditions, such as during adriver tip-in. Routine 400 may be performed as part of control routine300, specifically at 312.

At 402, it may be determined whether the amount of boost provided by theturbocharger is less than a threshold during a driver tip-in. Thus, itmay be determined whether a turbo lag condition is present. In someexamples, the threshold may be based on a desired boost amount. Forexample, at 402, it may be determined whether a difference between adesired and actual boost is below a threshold amount. Herein, thethreshold may be adjusted based on the amount of torque requested by thedriver. If the boost is not below the threshold, and an adequate amountof boost has been provided, the routine may end. If turbo lag isconfirmed, at 404, it may be determined whether the particulate filteris regenerating (or will be regenerating). Filter regeneration may beperformed if, for example, an amount of particulates stored in thefilter is above a threshold, and/or the duration of filter operation inthe storing mode is greater than a threshold.

If filter regeneration is confirmed, at 406, the routine may determinean amount of fuel to be late injected based on the boost level at thetime of torque request. For example, an amount of fuel injected may beincreased when the boost level is below the threshold. The amount offuel late injected may be an amount that may raise the exhausttemperature sufficiently such that the heated exhaust may then increaseturbine speed to produce the desired torque, and thereby reduce turbolag. By reducing the turbo lag, the boost desired in response to thetorque requested at driver tip-in may be provided. In an alternateembodiment, the amount of fuel late injected may be based on the amountof torque requested by the driver.

At 408, the amount of fuel late injected may be further adjusted basedon the exhaust temperature. In one example, the exhaust temperature maybe used to infer a filter temperature. Alternatively, the amount of fuellate injected may be adjusted based on filter temperature and/or anamount of stored particulates. The amount of fuel late injected may beadjusted, for example, to raise the exhaust temperature above athreshold where the filter may be regenerated and the storedparticulates may be burned off. The threshold may be adjusted to attaina desired filter temperature and/or based on an amount of particulatesstored in the filter at the time of regeneration. The adjustment mayinclude, for example, increasing an amount of fuel injected as theexhaust temperature or filter temperature decreases (for example,decreases below the threshold) and/or increasing the amount of fuelinjected as the amount of particulates stored in the filter increases.

At 410, the determined amount of fuel may be late injected upstream ofthe filter during an exhaust stroke of the engine cycle such that theinjected fuel is not combusted in the engine cylinder. Instead, anexothermic reaction may be generated at the filter thereby raising thefilter temperature and raising the temperature of the exhaust gasreaching the turbine. In one example, the filter may include a catalyzedwashcoat such that the fuel injected during the exhaust stroke isexothermically reacted in the filter with excess oxygen. The injectionmay be stopped, for example, in response to an increase in the boostabove the threshold (for example, the boost increasing to a levelenabling the requested torque to be provided), or the engine torqueincreasing above the requested torque. In some examples, the thresholdmay be based on a desired boost amount. For example, the injection maybe stopped when a difference between a desired and actual boost is abovea threshold. Alternatively, the injection may be stopped in response toan increase in exhaust temperature (or filter temperature) above athreshold and/or a drop in the amount of stored particulates below athreshold. Further still, in some embodiments, a subsequent engine fuelinjection (for example, during a subsequent engine cycle) may beadjusted based on the amount of fuel previously injected (for example,to maintain a desired air-fuel ratio).

In this way, by late injecting fuel upstream of a particulate filterunder selected boosted operating conditions, boost issues arising attip-in may be addressed during filter regeneration.

Now turning to FIG. 5, a routine 500 is illustrated for adjusting awastegate position to address SCR catalyst reductant mixing issues.Routine 500 may be performed as part of control routine 300,specifically at 316.

At 502, the routine may determine exhaust flow characteristics. Thesemay include, for example, an exhaust flow rate, an exhaust temperature,an amount of exhaust directed to the catalyst versus an amount ofexhaust recirculated to the engine intake via EGR (for example, viaLP-EGR and/or HP-EGR), etc. The routine may also determine injectiondetails, such as, an injection amount, an injection flow rate, and aninjection pressure. At 504, it may be determined whether more mixing ofthe exhaust gas and the injected reductant is required. As such, mixingconditions may be estimated or inferred from the determined exhaust flowdetails and reductant injection details. For example, higher injectionpressures may enable better mixing. Similarly, higher exhausttemperatures may enable better mixing due to an improved vaporization ofthe injected reductant. An engine controller may include a look-up tablespecifying a range of exhaust temperature, exhaust flow rate, turbinespeed, wastegate position, and injection pressure combinations whereinsubstantial reductant mixing may be enabled. In one example, mixingissues may be identified if the exhaust and injection parameters, asdetermined at 502, are outside the desired range/combination.Alternatively, mixing issues may be inferred if the wastegate positionis greater than a first threshold and the turbine speed is below asecond threshold.

If more mixing is required, at 508, the wastegate position may beadjusted to increase an amount of reductant that is directed to the SCRcatalyst via the turbine. In one example, reducing a wastegate openingmay increase reductant mixing. In comparison, if more mixing is notrequired, at 506, the wastegate position may be adjusted to decrease theamount of reductant that is directed to the SCR catalyst via theturbine. In one example, increasing a wastegate opening may decreasereductant mixing. However, it will be appreciated that changing theamount of reductant delivered via the turbine may not affect the netamount of reductant delivered to the catalyst.

In this way, an engine controller may be configured to inject reductantinto the exhaust upstream of the turbine, mix the injected reductantwith exhaust gas via the turbine, and deliver the mixed reductant to thedownstream catalyst. By injecting the reductant upstream of the turbine,the temperature difference of exhaust across the turbine may beadvantageously used to improve the vaporization of the reductant than,for example, if the reductant was injected downstream of the turbine.Specifically, the higher exhaust temperature upstream of the turbine maybe used to better vaporize the injected reductant, thereby improving itsmiscibility with exhaust gas. Additionally, the turbulent flow throughthe blades and vanes of the turbine may further atomize the injectedreductant and enable better mixing. Further still, by improving mixingof the injected reductant without an additional mixer, or mixingsection, component and cost reduction may be achieved. The well mixedreductant may then be delivered to the SCR catalyst at lower exhausttemperatures downstream of the turbine, thereby reducingover-temperature catalyst issues. Wastegate adjustments made herein maybe compensated for in the parent routine 300, at 326, as previouslyelaborated with reference to FIG. 3.

Now turning to FIG. 6, a routine 600 is illustrated for adjusting awastegate position to thereby adjust the SCR catalyst temperature to adesired catalyst temperature, or temperature range. Routine 600 may beperformed as part of control routine 300, specifically at 320.

At 602, it may be determined whether the SCR catalyst temperature (Tcat)is below a threshold temperature, or temperature range. If the catalysttemperature is below the threshold temperature, then at 604, the routinemay determine whether the non-wastegate temperature actuators arelimited. For example, if actuators other than the wastegate may beadjusted to influence catalyst temperature, then as a first approach,such other actuators may be used to address the temperature issue. Thus,if a temperature actuator other than the wastegate, such as injectiontiming, is available for modulation to thereby adjust the catalysttemperature and bring it to the desired temperature range, then at 606,the routine may address the catalyst temperature issues with thenon-wastegate temperature actuator.

In comparison, if all the non-wastegate temperature actuators arelimited (e.g., due to combustion stability limits, torque control,emission limits, etc.), then at 608, the routine may address thecatalyst temperature issue with a wastegate adjustment. Specifically,the wastegate opening may be adjusted (for example, increased) tothereby increase an exhaust flow to the catalyst via the wastegate. Inone example, the adjustment may be based on the catalyst temperature. Inanother example, the adjustment may be based on exhaust temperature, andthe catalyst temperature may be inferred from the exhaust temperature.In still another example, the adjustment may be based on a degree offilter regeneration of the upstream particulate filter. The adjustmentmay include, for example, increasing a wastegate opening when thecatalyst temperature is below the desired catalyst temperature, anddecreasing a wastegate opening when the catalyst temperature is abovethe desired catalyst temperature. In another example, the adjustment mayfurther include increasing the opening of the wastegate during filterregeneration. For example, during filter regeneration there may be arisk of over temperature conditions occurring in the downstream turbine(e.g., turbine 54). Thus, under certain conditions, the wastegateopening may be increased to avoid over temperature conditions duringregeneration.

The wastegate adjustment in response to SCR catalyst temperature beingbelow a desired temperature may enable a larger portion of exhaust gasto bypass the turbine and reach the catalyst directly. As such, duringpassage through the turbine, at least a portion of heat may be extractedfrom the heated exhaust by the turbine. Thus, the temperature of exhaustreaching the catalyst through the turbine may be lower than thetemperature of exhaust reaching the catalyst via the wastegate. Byincreasing the amount of heated exhaust reaching the catalyst via thewastegate during conditions when the catalyst is below the desiredoperating temperature, the temperature of the catalyst may be raised.Wastegate adjustments made herein may be compensated for in the parentroutine 300, at 326, as previously elaborated with reference to FIG. 3.In some examples, wastegate adjustments may further depend onturbocharger boost and speed. For example, the wastegate valve may beadjusted to avoid over temperature conditions in the turbocharger andmeet boost requirements.

In this way, a turbine wastegate may be advantageously used to adjust anamount of heated exhaust delivered to a downstream SCR catalyst, therebycontrolling the catalyst temperature. By adjusting an initial wastegateposition based on the operating mode of an upstream particulate filter,and thereafter adjusting the wastegate position to adjust an amount ofhot exhaust, as used during filter regeneration, that is delivered tothe catalyst via the wastegate, the catalyst temperature may becontrolled while co-coordinating the operation of the various emissioncontrol devices. By adjusting the injection of reductant upstream of theturbine based on the final wastegate position, as elaborated below inFIG. 7, the amount of reductant delivered to the catalyst may also becontrolled. By controlling the temperature and reductant dosage of anSCR catalyst, the catalyst performance may be improved and the NOxcontent of exhaust emissions may be reduced.

Now turning to FIG. 7, a routine 700 is illustrated for adjusting anamount of reductant injected upstream of the turbine responsive towastegate adjustments, to thereby adjust an amount of reductantdelivered to a downstream SCR catalyst. Routine 700 may be performed aspart of control routine 300, specifically at 324. In particular, thereductant injection may compensate for boost changes arising frompreceding wastegate adjustments.

At 702, the routine may determine an initial reductant injection amountbased on engine operating conditions. For example, the initial reductantinjection amount may be adjusted based on the boost estimated inresponse to the driver torque demand, the amount of reductant alreadypresent on the SCR catalyst, catalyst temperature, exhaust NOx levels,etc. At 704, the routine may determine if there are any changes inboost. For example, it may be determined if any boost changes havearisen, or are expected, due to the preceding wastegate adjustments (aselaborated in FIG. 3 at 312-322). Alternatively, it may be determined ifthere is any sudden and temporary change in boost (for example, a suddentemporary drop in boost). At 706, the initial reductant amount may beadjusted based on the change in boost. In one example, the adjustmentmay include temporarily decreasing an amount of reductant injected whenboost falls below a threshold (for example, during a sudden drop inboost). The injection adjustment may then be stopped when the boostreturns to the desired value. In alternate embodiments, the adjustmentmay include increasing reductant injection as wastegate openingdecreases, decreasing an amount of reductant injected as the wastegateopening increases, increasing reductant injection as turbine speedincreases, and/or increasing reductant injection in the presence ofboost. In this way, an engine controller may be configured to adjust anamount of reductant injected into the exhaust based on previouswastegate adjustments.

Now turning to FIG. 8, a routine 800 is illustrated for adjusting aratio of exhaust gas recirculated to the engine intake via the HP-EGRand the LP-EGR passages, during a filter regeneration operation, basedon engine operating conditions. Routine 800 may be performed as part ofcontrol routine 300, specifically at 328.

At 802, it may be determined whether HP-EGR is present or desired. Assuch, during HP-EGR, at least a portion of exhaust may be diverted fromupstream of the turbine, and downstream of the particulate filter, viathe HP-EGR passage, to the engine intake downstream of the compressor.In one example, HP-EGR may be present (or desired) due to exhaust NOxlevels being above a threshold. If HP-EGR is present, then at 804,filter regeneration details may be determined. These may include, forexample, an amount of regeneration, a rate of regeneration, exhausttemperature during regeneration, exhaust flow rate during regeneration,an amount of particulates stored, an expected duration of regeneration,etc. At 806, the routine may adjust an amount of diverted exhaust gasbased on the estimated filter operating conditions, such as the filtertemperature and/or filter regeneration. Specifically, in response toHP-EGR during filter regeneration, the routine may adjust an HP-EGRvalve to thereby adjust an amount and/or rate of HP-EGR based on theregeneration details.

In one example, if HP-EGR is present at the start of filterregeneration, in anticipation of the heated exhaust used during filterregeneration, the amount of exhaust gas recirculated to the engineintake from upstream of the turbine and downstream of the filter may bedecreased by decreasing the opening of an HP-EGR valve. For example, theamount of heated exhaust diverted along EGR passage 63 may be decreasedby reducing the opening of HP-EGR valve 29. Additionally, the EGR flowthrough the cooler bypass may be correspondingly adjusted. In oneexample, substantially no exhaust gas may be diverted to the engineintake via HP-EGR, for example, by completely closing the HP-EGR valve.By reducing the amount of heated exhaust that is recirculated to theengine intake during filter regeneration, the undesirable effects of hotEGR flow on exhaust NOx emissions and engine performance may be reduced.Additionally, the thermal demands on the EGR cooler may also be reduced,thereby improving engine fuel efficiency.

In another example, if HP-EGR is present at the end of filterregeneration, in anticipation of cooler exhaust used after filterregeneration, the amount of exhaust gas recirculated to the engineintake from upstream of the turbine and downstream of the filter may beincreased by increasing the opening of an HP-EGR valve. For example, theamount of heated exhaust diverted (along exhaust passage 63) may beincreased by increasing the opening of HP-EGR valve 29. Additionally,the EGR flow through the cooler bypass may be correspondingly adjusted.By increasing the amount of heated exhaust that is recirculated to theengine intake after passing through the filter, a clean EGR flow may beprovided to the intake, thereby reducing EGR cooler, EGR valve andintake manifold degradation and improving engine performance and exhaustemissions.

As such, exhaust temperature changes at the start and stop of filterregeneration may be larger than exhaust temperature changes in themiddle of filter regeneration. Consequently, corresponding EGRadjustments at the start and stop of filter regeneration may be largerthan exhaust temperature changes in the middle of filter regeneration.In one example, the EGR adjustments may be gradually adjusted based onan exhaust temperature profile.

In alternate embodiments, the adjustment may be made responsive to theoperating mode of the filter. For example, an amount of diverted exhaustgas may be increased when the filter is storing particulates (storingmode) and the amount of diverted exhaust gas may be decreased when thefilter is regenerating (regeneration mode). In yet another embodiment,the adjustment may be made responsive to filter temperature. Forexample, an amount of diverted exhaust gas may be increased when thefilter temperature is below a threshold and the amount of divertedexhaust gas may be decreased when the filter temperature is above thethreshold.

At 808, an amount of LP-EGR may be adjusted based on the changes to theamount of HP-EGR. Specifically, after a first amount of exhaust gas isdiverted from downstream of the particulate filter and upstream of theturbine to the engine intake system (HP-EGR), the amount based on a rateof particulate filter regeneration, a second amount of exhaust gas isdiverted from downstream of the particulate filter and downstream of theturbine to the engine intake system (LP-EGR), the second amount adjustedto counteract the adjustment of the first amount. Furthermore, the totalEGR flow may depend on whether particulate filter regeneration isoccurring or not, as described above with regard to FIG. 6.

In one example, the ratio of HP-EGR and LP-EGR may be adjusted tomaintain a net desired EGR rate or burned mass fraction or intake oxygenconcentration. In another example, the ratio may be adjusted to achievea desired manifold temperature. For example, if the amount of HP-EGRperformed while the filter is regenerating results in higher intakemanifold temperatures (for example, higher than a threshold), then theroutine may reduce the amount of HP-EGR and correspondingly increase anamount of LP-EGR. In another example, if the amount of HP-EGR performedwhile the filter is regenerating results in lower intake manifoldtemperatures (for example, lower than a threshold), then the routine mayincrease the amount of HP-EGR and correspondingly decrease an amount ofLP-EGR.

In this way, by adjusting an amount of HP-EGR and LP-EGR based on filterregeneration conditions, the operation of the various emission controldevices may be co-ordinated with EGR operations while improving exhaustemissions.

Note that the example control and estimation routines included hereincan be used with various engine and/or vehicle system configurations.The specific routines described herein may represent one or more of anynumber of processing strategies such as event-driven, interrupt-driven,multi-tasking, multi-threading, and the like. As such, various acts,operations, or functions illustrated may be performed in the sequenceillustrated, in parallel, or in some cases omitted. Likewise, the orderof processing is not necessarily required to achieve the features andadvantages of the example embodiments described herein, but is providedfor ease of illustration and description. One or more of the illustratedacts or functions may be repeatedly performed depending on theparticular strategy being used. Further, the described acts maygraphically represent code to be programmed into the computer readablestorage medium in the engine control system.

It will be appreciated that the configurations and routines disclosedherein are exemplary in nature, and that these specific embodiments arenot to be considered in a limiting sense, because numerous variationsare possible. For example, the above technology can be applied to V-6,I-4, I-6, V-12, opposed 4, and other engine types. The subject matter ofthe present disclosure includes all novel and non-obvious combinationsand sub-combinations of the various systems and configurations, andother features, functions, and/or properties disclosed herein.

1. A method of operating an engine including an emission control system,the emission control system comprising a catalyst downstream of aturbine of a boosting device and a reductant injector upstream of theturbine, comprising: injecting reductant into exhaust upstream of theturbine; mixing the injected reductant with exhaust gas via the turbine;and delivering the mixed reductant to the catalyst.
 2. The method ofclaim 1, wherein the emission control system further comprises aparticulate filter upstream of the reductant injector, and where thereductant includes urea.
 3. The method of claim 2, wherein the catalystis an SCR catalyst.
 4. The method of claim 1, further comprising,adjusting a wastegate of the turbine to control an amount of mixing ofthe reductant.
 5. The method of claim 4, wherein the wastegateadjustment includes reducing wastegate opening to increase reductantmixing.
 6. The method of claim 5, further comprising adjusting reductantinjection based on a change in boost.
 7. The method of claim 6, whereinthe injection adjustment includes temporarily decreasing an amount ofinjection when boost is decreased.
 8. A method of operating an engineincluding an emission control system, the emission control systemcomprising an SCR catalyst downstream of a turbocharger exhaust turbineand a reductant injector upstream of the turbine, the emission controlsystem further comprising a particulate filter upstream of the reductantinjector, the method comprising: injecting reductant into exhaustupstream of the turbine and downstream of the particulate filter, theinjection adjusted based on a boost operating condition; mixing theinjected reductant with exhaust gas via the turbine; and delivering themixed reductant to the SCR catalyst.
 9. The method of claim 8, whereinthe adjustment includes temporarily decreasing an amount of injectionwhen the amount of boost is decreased.
 10. The method of claim 8,further comprising, adjusting a turbocharger wastegate position toreduce wastegate flow when turbine speed falls below a threshold.
 11. Anemission control system for a turbocharged internal combustion enginecomprising: a reductant injector upstream of a turbocharger turbine; andan SCR catalyst downstream of the turbocharger turbine.
 12. The systemof claim 11, further comprising a particulate filter upstream of theturbine.
 13. The system of claim 11, further comprising an electroniccontroller configured to adjust an amount of reductant injected into theexhaust upstream of the turbine based on an amount of boost provided bythe turbocharger.
 14. The system of claim 13, further comprising an EGRpassage configured to route at least a portion of exhaust gas from theengine exhaust to the engine intake.
 15. The system of claim 14, whereinthe controller is configured to further adjust the amount of reductantinjected based on at least one of a catalyst temperature, an exhaust NOxlevel, and a turbocharger wastegate position.
 16. The system of claim15, wherein the adjustment includes increasing reductant injection aswastegate opening decreases, increasing reductant injection as turbinespeed increases, and/or increasing reductant injection in the presenceof a boost.